credential: add credential.*.username

Credential helpers can help users avoid having to type their
username and password over and over. However, some users may
not want a helper for their password, or they may be running
a helper which caches for a short time. In this case, it is
convenient to provide the non-secret username portion of
their credential via config.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

credential.c

@@ -65,6 +65,10 @@ static int credential_config_callback(const char *var, const char *value,
 
 	if (!strcmp(key, "helper"))
 		string_list_append(&c->helpers, value);
+	else if (!strcmp(key, "username")) {
+		if (!c->username)
+			c->username = xstrdup(value);
+	}
 
 	return 0;
 }

t/t0300-credentials.sh

@@ -234,4 +234,17 @@ test_expect_success 'do not match configured credential' '
 	EOF
 '
 
+test_expect_success 'pull username from config' '
+	test_config credential.https://example.com.username foo &&
+	check fill <<-\EOF
+	protocol=https
+	host=example.com
+	--
+	username=foo
+	password=askpass-password
+	--
+	askpass: Password for '\''https://foo@example.com'\'':
+	EOF
+'
+
 test_done

t/t5550-http-fetch.sh

@@ -113,6 +113,22 @@ test_expect_success 'http auth respects credential helper config' '
 	expect_askpass none
 '
 
+test_expect_success 'http auth can get username from config' '
+	test_config_global "credential.$HTTPD_URL.username" user@host &&
+	>askpass-query &&
+	echo user@host >askpass-response &&
+	git clone "$HTTPD_URL/auth/repo.git" clone-auth-user &&
+	expect_askpass pass user@host
+'
+
+test_expect_success 'configured username does not override URL' '
+	test_config_global "credential.$HTTPD_URL.username" wrong &&
+	>askpass-query &&
+	echo user@host >askpass-response &&
+	git clone "$HTTPD_URL_USER/auth/repo.git" clone-auth-user2 &&
+	expect_askpass pass user@host
+'
+
 test_expect_success 'fetch changes via http' '
 	echo content >>file &&
 	git commit -a -m two &&